1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, more particularly to a structure of a lateral transistor suitable for implementing a high-density monolithic integration on a semiconductor substrate.
2. Description of the Related Art
A structure merging a power transistor and its control circuit on the same semiconductor chip so as to form a semiconductor integrated circuit is known. In such a power IC, sometimes the power transistor is made by a vertical npn transistor and the control circuit by lateral pnp transistors, the lateral pnp transistor operating with relatively lower power than the vertical npn transistor. An example of the structure of the earlier lateral pnp transistor employed in these semiconductor integrated circuits (power ICs) is shown in FIGS. 1A and 1B. That is, the earlier lateral pnp transistor embraces a semiconductor substrate 1, an n-type first buried region 22 formed on the semiconductor substrate 1, an n-type first base region 33 formed over the entire surface of the semiconductor substrate 1, an n-type first plug region 4 so formed that the bottom of the first plug region 4 reaches to the first buried region 22, a p-type first emitter region 6 and a p-type first collector region 7 formed in and at the surface of the first base region 33, and an n-type first base contact region 9 formed in and at the surface of the first plug region. The lateral pnp transistor constructed in this manner encompasses further a field insulating film 86 on the top surface. And, a first emitter wiring 11, a connecting wiring 12, and a first base wiring 14 contact through contact holes in the field insulating film 86 with the first emitter region 6, the first collector region 7 and the first base contact region 9. The connecting wiring 12 serves as a first collector wiring and is connected to the base electrode of the vertical npn transistor having a high maximum operating voltage, though the illustration of the vertical npn transistor is omitted in FIGS. 1A and 1B.